1. Field of the Invention
This invention relates to a two part silicone sealant which cures upon mixing of the two parts to give an ultra low modulus elastomeric sealant.
2. Background Information
British Patent Specification 1,308,985, published Mar. 7, 1983, discloses a method of curing room temperature vulcanizing silicone rubber containing acetoxy-silicon bonds, which method adds sodium alumino silicate having adsorbed water. The water from the aluminosilicate causes the silicone rubber to cure even if the composition is not open to atmospheric moisture.
A silicone composition which cures upon exposure to moisture in the air is described in U.S. Pat. No. 3,817,909, issued Jun. 18, 1974. This composition is obtained by mixing a hydroxyl endblocked polydiorganosiloxane, non-acidic, non-reinforcing filler, a difunctional acetamidosilane, and an aminoxysilicon compound.
A low modulus room temperature vulcanizable silicone elastomer with improved slump characteristics is taught in U.S. Pat. No. 3,996,184, issued Dec. 7, 1976. The composition contains hydroxyl endblocked polydimethylsiloxane, non-acidic, non-reinforcing filler, methylvinyldiacetamidosilane, aminoxysilicon compound, and a selected polar solvent. The sealants are useful in sealing joints wherein the building materials sealed by the material can expand and contract without breaking the seal.
An organopolysiloxane composition which rapidly hardens to the elastomeric state is disclosed in U.S. Pat. No. 4,508,888, issued Apr. 2, 1985. The composition comprises a polyhydroxylated polysiloxane, a polyacyloxysilane cross-linking agent, and a hardening accelerator comprising water and an alkali or alkaline earth metal phosphate and/or polyphosphate.
A silicone sealant having an improved skinover time is taught in U.S. Pat. No. 4,978,706, issued Dec. 18, 1990. The composition consists essentially of hydroxyl containing polydiorganosiloxane, diacetamido functional silane, and tetraoximino functional silane. The composition can also contain non-acidic, non-reinforcing filler.
Typical one-part silicone sealant formulations cure by the reaction of moisture in the air. The curing process starts at the surface and gradually proceeds inward. The time required to reach full cure varies from a few days to several weeks, depending upon the system. Typically, all one-part systems are packaged to minimize exposure to atmospheric moisture as this will result in premature curing. In some instances, excess reactive groups are added to react with incoming moisture, but still produce a curable one-part formulation. This invention describes how the introduction of controlled amounts of reactive hydroxyl groups, without catalyst, can take advantage of any excess reactive groups to prepare a two-part formulation that, when the two parts are mixed, rapidly cures to an ultra-low modulus silicone sealant without the need for moisture from the atmosphere.